Epoxidation of aldrin by rainbow trout liver microsomes Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qf85nf15q

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  • Assay conditions and analytical methods established for the study of epoxidation of the insecticides aldrin and heptachlor, by rat liver microsomes have been employed to study the same reaction catalyzed by trout liver microsomes. At 37° C and pH 8.0, rainbow trout liver microsomes, incubated with 54.8 millimicromoles of either aldrin or heptachlor in the presence of reduced triphosphopyridine nucleotide (NADPH) and oxygen, produced only 0.36 milli-micromole of the corresponding expoxides, dieldrin and heptachlor epoxide. This was only 7.2% of the amount produced by similar assays with male rat liver microsomes. Increasing the microsomal protein and extending the incubation time failed to increase the epoxide yield of the fish microsomes. The same result was obtained when incubations were carried out at 2, 11, and 22° C, within a pH range of 6.0 to 8.5. Varying the substrate level from 5 to 100 millimicromoles did not affect the activity. Dieldrin formation remained unchanged when a large excess of an NADPH-generating system or six micromoles of either Fe(II), Mn(II), Co(II), Mg(II) or FMN was added. Incubation of aldrin with freshly prepared trout liver slices instead of microsomes failed to show any improvement in epoxidation. However, no dieldrin was detected when either heat-denatured microsomes, snake venom-treated preparation, steapsin-treated preparation or liver acetone powder was used. Activities of the components of the microsomal electron transport system, which plays a vital role in epoxidation, were measured. Results indicated their presence in significant levels in trout liver microsomes. Aldrin and heptachlor conversions by male rat liver micro-somes were enhanced two to four times by the addition of either an acetone powder preparation, the supernatant fraction above the 78,000 X g pellet, or microsomes, of trout liver. A reaction is said to be enhanced, when the activity of the combined system is greater than the sum of those of the separate preparations. However, no enhancement was observed when an inactive rat preparation, such as a rat liver acetone powder preparation, was used in combination with a trout fraction. The extent of enhancement in epoxidation depended primarily on the basal activity of the rat liver microsomes. Furthermore, the enhancing ability of the fish fractions was abolished by treating them with heat, snake venom, or steapsin. Of the three microsomal electron transport component activities tested, only that involved in neotretazolium (NT) reduction was enhanced by combining rat and trout liver microsomes in the assays. NADPH-cytochrome c and dichlorophenol indophenol (DCPIP) reductase activities were additive in the combined systems. NT reduction is a test reaction for component X₁ in the NADPH-dependent electron transport chain of liver microsomes. The parallel relationship between enhancement of NT reduction and epoxidation and their relative positions in the established sequence of reactions in the NADPH-dependent chain indicates that the enhancement in epoxidation is brought about by an increase in X₁ relative to the epoxidative enzyme(s) in the combined systems. The evidence collected in this research leads to the conclusion that the low epoxidative activity in trout liver microsomes is a result of a deficiency in the epoxidative enzyme(s).
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  • File scanned at 300 ppi using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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